Great Smoky Mountains National Park.

ASHEVILLE -- For the third straight year, Great Smoky Mountains National Park has achieved a ranking it could do without: as one of 10 most-polluted national parks in the country. The National Parks Conservation Association, which compiles the ranking, blames traffic -- 10 million annual visitors -- and pollution from coal-burning Tennessee Valley Authority plants to the west. TVA has launched an $800 million cleanup.